Combining the use of antibodies specific to fast and slow muscle myosins with muscle protein chemistry, we plan to investigate the neurogenic and myogenic controls on myofibrillar protein synthesis. Specifically, we will examine (1) whether during normal embryogenesis, fiber types are interconvertible; (2) whether alterations of fiber types may lead to temporary architectural and functional problems for the muscle; (3) whether heterogeneity exists within the fast and slow myosin classes. In addition, (4) we will continue work on an in vitro system for examining the control of changes in fiber types. Our objective is elucidation of the mechanisms by which neural impulses can control the expression of genes in muscle fibers. Ultimately, we wish to apply a better understanding of the normal controls on muscle gene activity to an investigation of the causes of morphological and biochemical abnormalities found in human neuromuscular diseases.